<template>
  <el-select :value="valueTitle" :clearable="clearable" @clear="clearHandle">
    <el-option :value="valueTitle" :label="valueTitle" class="options">
      <el-tree
        id="tree-option"
        ref="selectTree"
        :accordion="accordion"
        :data="options"
        :props="props"
        :node-key="props.value"
        :default-expanded-keys="defaultExpandedKey"
        @node-click="handleNodeClick">
      </el-tree>
    </el-option>
  </el-select>
</template>

<script>
    export default {
      name: 'el-tree-select',
      props: {

            // 配置项
        props: {
          type: Object,
          default: {
            value: 'id',             // ID字段名
            label: 'title',         // 显示名称
            children: 'children'    // 子级字段名
          }
        },

            // 选项列表数据(树形结构的对象数组)
        options: { type: Array, default: [] },

            // 初始值
        value: { type: String, default: null },

            // 可清空选项
        clearable: { type: Boolean, default: true },

            // 自动收起
        accordion: { type: Boolean, default: false }

      },
      data () {
        return {
          valueId: '',
          valueTitle: '',
          defaultExpandedKey: []
        }
      },
      mounted () {
        this.valueId = this.value    // 初始值
        this.initHandle()
      },
      methods: {
            // 初始化值
        initHandle () {
          if (this.valueId) {
            this.valueTitle = this.$refs.selectTree.getNode(this.valueId).data[this.props.label]     // 初始化显示
            this.$refs.selectTree.setCurrentKey(this.valueId)       // 设置默认选中
            this.defaultExpandedKey = [this.valueId]      // 设置默认展开
          }
          this.initScroll()
        },

            // 初始化滚动条
        initScroll () {
          this.$nextTick(() => {
            let scrollWrap = document.querySelectorAll('.el-scrollbar .el-select-dropdown__wrap')[0]
            let scrollBar = document.querySelectorAll('.el-scrollbar .el-scrollbar__bar')
            scrollWrap.style.cssText = 'margin: 0px; max-height: none; overflow: hidden;'
            scrollBar.forEach((ele) => { ele.style.width = 0 })
          })
        },

            // 切换选项
        handleNodeClick (node) {
          this.valueTitle = node[this.props.label]
          this.valueId = node[this.props.value]
          this.$emit('getValue', this.valueId)
          this.defaultExpandedKey = []
        },

            // 清除选中
        clearHandle () {
          this.valueTitle = ''
          this.valueId = null
          this.defaultExpandedKey = []
          this.clearSelected()
          this.$emit('getValue', null)
        },

            // 清空选中样式
        clearSelected () {
          let allNode = document.querySelectorAll('#tree-option .el-tree-node')
          allNode.forEach((element) => element.classList.remove('is-current'))
        }

      },

      watch: {
        value () {
          this.valueId = this.value
          this.initHandle()
        }
      }
    }
</script>

<style scoped>
  .el-scrollbar .el-scrollbar__view .el-select-dropdown__item{
    height: auto;
    max-height: 274px;
    padding: 0;
    overflow: hidden;
    overflow-y: auto;
  }
  .el-select-dropdown__item.selected{
    font-weight: normal;
  }
  ul li >>>.el-tree .el-tree-node__content{
    height:auto;
    padding: 0 20px;
  }
  .el-tree-node__label{
    font-weight: normal;
  }
  .el-tree >>>.is-current .el-tree-node__label{
    color: #409EFF;
    font-weight: 700;
  }
  .el-tree >>>.is-current .el-tree-node__children .el-tree-node__label{
    color:#606266;
    font-weight: normal;
  }
</style>
